1. Field of the Invention
The present invention relates to antenna structures, and, more particularly, to a beam steering antenna structure.
2. Description of Related Art
The transmission paths of electromagnetic waves often encounter the blockage of large building in cities and thus result in multi-path fading. As such, presently there exist many technical improving means and the so-called Smart Antenna has become mainstream that is designed to eliminate the transmission blockage mentioned above.
Smart antennas use the characteristic of Spatial Diversity to differentiate users and signals from different locations/positions for achieving the diversity gain. In other words, Smart antennas use narrower beams for receiving and transmitting signals to obtain greater power for communication, whereas the signals transmitted within the range of non-narrow beams are suppressed by narrower beams, thus reducing the intensity of noise signals in the ambient environment to obtain a greater signal gain. To change the direction of beam transmission, Smart antennas typically use active elements to alter the type of radiation fields of electromagnetic waves, thereby achieving the spatial diversity and realizing the Spacial Division Multiple Access mechanisms which have the impact of time delay spread and multipath fading to increase transmission efficiency and coverage and thus improve the quality and quantity of communication.
Typically, the means of altering antenna beams include using mechanical scanning or phased array antenna techniques to switch the direction of beam transmission. However, the former method has the disadvantage of low speed and the latter requires a complex feed-in structure and a phase shifter in order to control the phase of each of the antenna elements and thus is costly and inconvenient to apply. Furthermore, the current technologies propose an adaptive antenna which employs the digital signal processing and the concept of array antennas, in which the direction of signals is tuned up and the direction of noise signals is tuned down to intensify the beams in the direction of signals while reducing the impact of noise signals. However, the control of beam field type requires the digital signal processing in the basic frequency and thus has higher hardware and technology demands for practical applications.
Additionally, there has been an directional antenna structure 1 that employs the Cylindrical Electromagnetic bandgap proposed by H. Boutayeb et al. published in the Periodicals IEEE Transactions on Antennas Propagation in an article “Analysis and design of a cylindrical EBG-based directive antenna.” As depicted in FIG. 1, the directional antenna structure 1 is composed of an antenna 12 and multiple coil metallic wires 14 winding around the core of the antenna 12, wherein two electrodes 13 are disposed between the ring upon rings of the metallic wires 14 for the control of two electrodes 13, to either form a conductive equivalent continuous metallic wire that prevents electromagnetic waves from transmission, or to form a non-bias voltage equivalent discontinuous metallic wire for transmission, thereby controlling directions of the beam radiation. Yet, not only the processing of metallic wire is complex and laborious but also greater power consumption will be required to effectively block electromagnetic waves from spreading out.
Therefore, it is desirable and highly beneficial to provide a more effective and ideal design of the antenna structure capable of overcoming the drawbacks as encountered in prior techniques.